The invention relates to the continuous casting of metals. It relates more particularly to thin metal strip continuous casters of the type called xe2x80x9ctwin-roll castersxe2x80x9d.
The casting of thin metal strip a few mm in thickness directly from liquid metal (steel, stainless steel and other ferrous alloys, and copper, for example) may take place in a caster called a xe2x80x9ctwin-roll casterxe2x80x9d, supplied with liquid metal from a tundish by means of a pouring nozzle. The caster includes a mold whose casting space is bounded on its long sides by a pair of internally cooled rolls, having parallel horizontal axes and rotating about these axes in opposite directions, and on its short sides by closure plates made of refractory material, called xe2x80x9cside wallsxe2x80x9d, which are applied by thrust members against the flat ends of the rolls. Solidification of the liquid metal occurs against the cooled cylindrical surfaces of the rolls, by forming solidified shells which are made to join in the region of the nip (the region where the distance separating the surfaces of the rolls is a minimum) in order to form the strip, which is continuously extracted from the casting space. In some casters (which generally cast somewhat thicker products), the rolls may be replaced by moving cooled belts, which have been given a curved shape at the entrance of the casting space. These casters also have side walls similar to those of twin-roll casters and means for applying these side walls against the end faces of the belts. They are usually called xe2x80x9ctwin-belt castersxe2x80x9d.
Conventionally, each side wall is made as follows. It firstly comprises a support plate made of a material preferably having good insulating properties, such as silica. Usually, it is fastened on its rear face (the one facing outwards from the casting space) to a metal baseplate on which the thrust members act. However, if the support plate has sufficient mechanical strength and rigidity, provision may be made for the thrust members to exert their action directly on the support plate. Placed on the front face of this support plate is the active part of the side wall, that is to say the material or materials which are intended to come into contact with the rolls and with the liquid metal. Very often, the external regions of this active part, which have to come into contact with the rolls or be in the vicinity of the nip, are made of a first material exhibiting good properties of resistance to abrasion and to corrosion by the liquid metal, such as SiAlON(copyright) or silicon carbide, and the central region of this active part, which has to be in contact with the liquid metal, is made of a second material exhibiting good insulating properties, such as silica foam. Often the element or elements making up the external regions are referred to by the term xe2x80x9cinsertxe2x80x9d and the element or elements forming the rest of the side wall by the term xe2x80x9ccorexe2x80x9d. Before starting the casting run, the side walls are preheated, for the purpose of preventing metal from solidifying on their active part when the casting space is being filled with liquid metal.
The side walls are of paramount importance in the success of twin-roll casting of metal strip, especially steel strip. Poor sealing of their contacts with the edges of the rolls may lead to exfiltration of liquid metal out of the casting space, which compromises the regularity of the operation of the plant, and hence the quality of the strip. In extreme cases, such exfiltration may result in the casting run being stopped. Likewise, rupture during casting of one of its elements, or deconsolidation of the many elements making up the active face, result in the casting run being immediately stopped. Very particular attention must therefore be paid to the choice of the materials for the side walls, some of which (in particular, the materials used for the insert) are very expensive. Likewise, the assembly of the side wall, and in particular the production of its active part, is a complex operation which has to be carried out by highly qualified and careful operators, and this assembly (and, after assembly the drying of the refractories and bonding materials used) requires a great deal of time. The side walls can only be used for a single casting run, after which they are dismantled, and at least their active part is discarded. For these reasons, the side walls constitute one of the main elements in the operating cost of a thin strip twin-roll caster (or, in general, a plant for casting between two moving cooled walls), and any technical advance which would make it possible to reduce the expenditure of time and of material which are associated with them, without impairing their performance or their reliability, is eminently desirable.
The object of the invention is to propose a design of the side walls of a caster for casting thin metal strip between two moving cooled walls whose manufacturing and operating cost is substantially reduced compared with side walls of conventional design.
For this purpose, the subject of the invention is a side wall for closing off the casting space of a caster for continuously casting thin metal strip between two moving cooled walls, especially a xe2x80x9ctwin-roll casterxe2x80x9d or a xe2x80x9ctwin-belt casterxe2x80x9d, of the type comprising a support plate, on the rear face of which plate thrust members exert their action, for the purpose of applying said side wall against the end faces of said cooled walls, optionally via a metal baseplate fastened to the rear face of the support plate, and an active face placed against the front face of the support plate, the lateral portions of which are intended to be worn away on contact with said end faces of said cooled walls to a maximum depth xe2x80x9cexe2x80x9d and over a width xe2x80x9c1xe2x80x9d, the support plate and the active part being brought into contact with each other in a manner allowing them to be separated non-destructively, characterized in that the front face of the support plate has, in its central part, a recess, the depth of which is greater than xe2x80x9cexe2x80x9d, and in that the external edges of said front face have a general shape which matches that of the external edges of the active part and have a width of less than xe2x80x9c1xe2x80x9d.
As will have been understood, the invention consists in designing the side wall so as to allow its active part to be used no longer for only one casting run, but for two, by simply inverting this active part between the two casting runs. For this purpose, the front face of the support plate must especially be given a special shape. Thus, a considerable amount of time is saved in preparing the side wall before the second casting run of the series.